Designers and manufacturers in the aerospace industry are constantly trying to improve fuel efficiency, product performance and constantly trying to reduce the manufacturing and service costs. Efficiency can be improved by further weight reduction. One way of obtaining this is by improving the relevant material properties, so that the structure made from that alloy can be designed more effectively or will have overall a better performance. By having better material properties, also the service cost can be significant reduced by longer inspection intervals of the aeroplane. Lower wing plates are typically made from AA2324 in the T39 temper. For fuselage skin, typically AA2024 in the T351 temper was used. This because these alloy in these temper showed the requested material properties under tensile loading, i.e. acceptable strength levels, high toughness and low crack growth propagation. Nowadays, new more efficient aeroplanes are designed, leading to wish for improved material properties.
U.S. Pat. No. 5,652,063 discloses an AA2000-series alloy with a Cu/Mg ratio between 5 and 9 and strength of more than 531 MPa. The alloy can be used both for lower wing plate and for fuselage skin. This alloy is particularly intended for supersonic aircraft.
U.S. Pat. No. 5,593,516 discloses an AA2000-series alloy wherein the copper (Cu) and magnesium (Mg) levels are kept preferably below the solubility limit. Preferably, [Cu]=5.2−0.91[Mg]. In U.S. Pat. Nos. 5,376,192 and 5,512,112, originating from the same initial US patent application, the addition of silver (Ag) levels of 0.1-1.0 weight % has been disclosed.
U.S. patent application US2001/0006082 discloses an M2000-series alloy especially suitable for the lower wing, without dispersoid forming elements like Zirconium (Zr), Chromium (Cr), or Vanadium (V). It is mentioned also that advantages are achieved by a mandatory Cu/Mg ratio of above 10.
For new designed aeroplanes, there is a wish for even better properties than the above-described alloys have, in order to design more cost and environmental effective aeroplanes. Accordingly, a need exist for an aluminium alloy capable of achieving the improved proper property balance in the relevant product form.